The current application shares some specification and figures with the following commonly owned and concurrently filed applications in the following table, all of which are hereby incorporated by reference:
1. Field of the Invention
The present invention relates generally to a petroleum well having a downhole modem, and in particular, to a downhole electronics module having one or more sensors which communicate with the surface, whereby the electronics module and sensors are powered using the tubing string and casing as a conductor.
2. Description of Related Art
Several methods have been devised to place electronics, sensors, or controllable valves downhole along an oil production tubing string, but all such known devices typically use an internal or external cable along the tubing string to provide power and communications downhole. It is, of course, highly undesirable and in practice difficult to use a cable along the tubing string either integral to the tubing string or spaced in the annulus between the tubing string and the casing. The use of a cable presents difficulties for well operators while assembling and inserting the tubing string into a borehole. Additionally, the cable is subjected to corrosion and heavy wear due to movement of the tubing string within the borehole. An example of a downhole communication system using a cable is shown in
U.S. Pat. No. 4,839,644 describes a method and system for wireless two-way communications in a cased borehole having a tubing string. However, this system describes a communication scheme for coupling electromagnetic energy in a TEM mode using the annulus between the casing and the tubing. This inductive coupling requires a substantially nonconductive fluid such as crude oil in the annulus between the casing and the tubing. Therefore, the invention described in U.S. Pat. No. 4,839,644 has not been widely adopted as a practical scheme for downhole two-way communication. Another system for downhole communication using mud pulse telemetry is described in U.S. Pat. Nos. 4,648,471 and 5,887,657. Although mud pulse telemetry can be successful at low data rates, it is of limited usefulness where high data rates are required or where it is undesirable to have complex, mud pulse telemetry equipment downhole. Other methods of communicating within a borehole are described in U.S. Pat. Nos. 4,468,665; 4,578,675; 4,739,325; 5,130,706; 5,467,083; 5,493,288; 5,576,703; 5,574,374; and 5,883,516. Similarly, several permanent downhole sensors and control systems have been described in U.S. Pat. Nos. 4,972,704; 5,001,675; 5,134,285; 5,278,758; 5,662,165; 5,730,219; 5,934,371; and 5,941,307.
Side-pocket mandrels coupled to the production tubing are known for receiving wireline insertable and retrieval gas lift valves. Many gas lift wells have gas lift valves incorporated as an integral part of the tubing string, typically mounted to a tubing section. However, wireline replaceable side pocket mandrel type of gas lift valves have many advantages and are quite common (such as made by Camco or Weatherford.) See U.S. Pat. Nos. 5,782,261 and 5,797,453. Gas lift valves placed in a side pocket mandrel can be inserted and removed using a wireline and kickover tool either in top or bottom entry. Therefore, it is common practice in oilfield production to shut off production of the well every three to five years and use a wireline to replace gas lift valves. Often, an operator has a good estimate of which valves in the well have failed or degraded and need to be replaced.
It would, therefore, be a significant advance in the operation of gas lift wells if an alternative to the conventional bellows type valve were provided, in particular, if the tubing and casing could be used as communication and power conductors to control and operate such a gas lift valve. It would also be advantageous to have sensors and electronics downhole that are powered and communicate using the tubing string and the casing. These sensors and electronics could then be used cooperatively with the controllable gas lift valves to more efficiently operate the well.
All references cited herein are incorporated by reference to the maximum extent allowable by law. To the extent a reference may not be fully incorporated herein, it is incorporated by reference for background purposes and indicative of the knowledge of one of ordinary skill in the art.
The problems outlined above with sensing and communicating downhole in an oil or gas well are addressed by the sensors and electronics module according to the system and method of the present invention. Broadly speaking, an oil or gas well includes a cased wellbore. The wellbore is cased with casing that extends substantially throughout the length of the bore and is held in place by cement between an exterior surface of the casing and the bore. A tubing string is positioned within and longitudinally extends within the casing. An electronics module is coupled to the tubing and includes one or more sensors that work cooperatively with the electronics module to monitor and determine various downhole conditions. Examples of the downhole conditions that can be monitored include tubing fluid pressure, tubing fluid temperature, annulus fluid pressure, annulus fluid temperature, fluid flow rates, valve positions, acoustic data, and seismic data. The electronics module and sensors are powered and communicate with the surface using the tubing and casing as conductors.
In more detail, a surface computer includes a master modem that can impart a communications signal to the tubing. The signal is preferably applied below a current limiting device such as a ferromagnetic choke positioned concentrically around the tubing. Low voltage alternating current (AC) power is also supplied to the tubing string below the current limiting device. In a preferred form, the casing is used as a ground return conductor, although an open hole ground to earth is also practical. The power and communications signals are received downhole by the electronics module and sensors. The electronics module includes a downhole slave modem for communicating the sensor measurements to the surface computer. Preferably, the electronics module and sensors are inserted as a wireline retrievable module into a side pocket mandrel in the tubing string. Alternatively, the electronic module and sensors may be mounted directly on the tubing.
The ferromagnetic chokes positioned around the tubing act as a series impedance to current flow in the tubing. In a preferred form, an upper ferromagnetic choke is placed around the tubing below a casing hanger near the top of the wellbore. A lower ferromagnetic choke is placed around the tubing downhole, and the electronics module is electrically coupled to the tubing just above the lower ferromagnetic choke. When power and communication signals are applied to the tubing below the upper ferromagnetic choke, the signal is effectively blocked from traveling beyond the lower or upper ferromagnetic chokes. This creates a potential between the tubing and a ground that is then used to power and communicate with the electronics module in the wellbore.
In a preferred form, the surface computer can be coupled via its surface master modem, not only to the downhole slave modem, but also to a variety of other data sources outside of the wellbore. These data sources could provide information, for example, on measurements of oil output and measurements of compressed gas input. The measurements could then by used by the surface computer to determine an optimum operating state of the oil well. In a preferred embodiment, the computer could then control the operation of the oil well by varying the amounts of compressed gas input, introducing needed chemicals into the oil well, or controlling downhole valves such as gas lift valves.